Field of the Invention
The present invention relates to a vertical machining center.
Discussion of the Background
When a vertical machining center is used to machine a workpiece on its top surface and side surfaces, which is what is called five-face machining, all steps of the machining are performed on the single vertical machining center by utilizing an angle attachment or an angle tool holder to change an axis orientation of a tool at right angles. The top surface of the workpiece is machined using a normal tool oriented downward. The side surfaces of the workpiece are subjected to what is called angle machining using a tool oriented horizontally by a mechanism to change the axis orientation of the tool spindle. Thus, all the steps of the machining of the workpiece are performed on the single vertical machining center.
Here, the angle attachment is a unit designed exclusively for a relatively large-sized machine. The angle attachment in general has a function to automatically change a tool to be attached to the attachment, and a function to turn and position the attachment on a horizontal plane so as to change the orientation of the tool attached to the attachment. As a result, the unit itself is enlarged and rarely applied to a small-sized machine.
In contrast, the angle tool holder serves for a small-sized machine. The angle tool holder is a tool holder including a spindle perpendicular to the axis of a tool spindle to which the tool holder is attached. In a mechanism to automatically change a normal tool, the angle tool holder is designed to be automatically changeable with respect to the tool spindle in the same manner as that of the normal tool. Some angle tool holders have such a function that, after each angle tool holder is held by the tool spindle, the orientation of the tool of the angle tool holder on a horizontal plane is changed to implement machining of a plurality of side surfaces.
In Japanese Patent No. 4565199 and Japanese Patent No. 4542626, the Applicant has disclosed an angle tool holder clamping unit for an angle tool holder and an angle tool holder mountable in a vertical machining center.